1. Field of the Invention
The present invention relates to a system using the RFID technique.
2. Description of the Prior Art
To access an RFID tag in the RFID (Radio Frequency Identification) technique, an RFID reader/writer transmits a carrier wave to the RFID tag through an RFID antenna connected to the RFID reader/writer. Receiving a carrier wave, the RFID tag reads data held in it and returns the data, for example. Or, receiving a carrier wave, the RFID tag writes data.
Sometimes, a plurality of RFID antennas are used in order to widen the read range for an RFID tag. In that case, an RFID antenna changer is introduced between an RFID reader/writer and RFID antennas. An RFID antenna changer connects one RFID reader/writer and a plurality of RFID antennas, and changes an antenna connected to the RFID reader/writer so that one antenna is activated among the plurality of antennas. Thus, one RFID reader/writer performs writing and reading through the activated RFID antenna.
However, according to the above-described method in which RFID antennas are changed and used one by one, the time required for reading becomes longer as the number of RFID antennas becomes larger. Thus, to shorten the read time, a plurality of RFID reader/writers are introduced and each RFID reader/writer is connected with a plurality of RFID antennas so that the plurality of RFID reader/writers are operated in parallel to perform reading. However, sometimes a combination of RFID antennas used at the same time causes interference between those RFID antennas, thus reducing the read rate.
Thus, Japanese Un-examined Patent Laid-Open No. 2005-157645 describes a technique in which reading order is determined in advance not to activate two adjacent RFID antennas at the same time. And, active RFID antennas are changed successively in that order to prevent interference between RFID antennas.